Water generator oscillating due to rapid flow of fluid

ABSTRACT

A prime mover for extracting power from moving water is described comprising a body which is caused to oscillate in water by reversing the direction of thrust generated by at least one submerged control member e.g. a hydroplane or rotating cylinder protruding from a side of the body. Preferably, the prime mover comprises an open bottomed tank which when it oscillates alternately compresses and decompresses a fluid inside it between a closed top of the tank and the water surface. Preferably the fluid is air. Other energy removal schemes can be combined with the prime mover to generate power.

BACKGROUND OF THE INVENTION

This invention relates to a prime mover, an apparatus and method forextracting power from moving water such as tidal flows and rivercurrents.

Hitherto, this has generally been proposed or achieved by means ofturbines analogous to underwater windmills. The blades of thesewindmills rotate as a result of the water flow about a horizontal orvertical axis at low speeds of the order of 10 to 30 revolutions perminute and at high torque. Gearboxes are required to transfer rotationat such speeds to the high speeds required for electrical generators.The gearboxes are large, complex and expensive with high power losses.The gearboxes also suffer from reliability problems and are difficult tomaintain, particularly when located under water.

GB1604372 discloses a device for utilising tidal energy which comprisestwo cylindrical tank members fitting slidably inside one another. Thedevice is supported on a tripod resting on the seabed. A flotationcollar renders the outer tank buoyant so that it rises and falls withthe water level as a result of which air within the tanks is compressedby their relative movement. Connections provided in the cover of theinner tank allow the compressed air to be used to drive an air turbinesituated at a remote location.

The current invention aims to provide a prime mover (for convertingnatural energy into mechanical power), an apparatus and a method fortransferring kinetic energy from slow moving water. The prime mover canbe used with any suitable energy removal scheme. For example it can beused to produce electrical energy directly or to provide a useful formof mechanical movement. In a further aspect of the invention, kineticenergy from slow moving water is transferred into kinetic energy of afluid travelling at high speed. Preferably the fluid is air.

According to a first aspect of the invention there is provided a primemover for extracting power from moving water comprising a body which iscaused to oscillate relative to the water by reversing the direction ofthrust generated by at least one submerged control member protrudingfrom a side of the body.

Whilst this prime mover is ideally suited for extracting energy fromflowing water, extraction from other flowing fluids is possible and theterm “water” should be interpreted as covering other flowing liquids andgases throughout this document.

Preferably, at least one control member protrudes from each side of thebody.

Preferably, the shape of the body is such that water is caused to travelfaster over a portion of the surface of the body and in which one ormore protruding control members are positioned at that portion of thesurface of the body.

Preferably, the body comprises curved sides which orientate the bodywith respect to a flow of water so that the control member or membersare substantially perpendicular to the direction of flow of the movingwater.

Preferably, the control member(s) is generally planar.

Preferably, the shape of the sides is symmetrical.

Preferably, the sides of the body are convex.

Preferably, at least one second protruding control member is providedfixed with respect to the body and arranged so that when the directionof thrust of a first reversible protruding control member is reversed,the angle of the second fixed control member with respect to the flow ofwater is altered so that the action of the water on that second fixedmember. Thus the control member acts like a tail plane of an aircraft.

Preferably, the fixed second control member is positioned at a point onthe body at which the velocity of the water flowing past the body is ator near a maximum.

Preferably, the first reversible control member is spaced laterally fromit in the direction of the water flow. Preferably, the reversiblecontrol member is downstream of the fixed control member. This is muchlike a tail plane on an aircraft.

Preferably, one or more control members comprise hydroplanes whereby thedirection of thrust is reversed by reversing the angle of inclination ofat least one hydroplane.

Preferably, the distribution of control members on opposing sides of thebody is symmetrical.

Preferably, the body is elongate and tends to orientate itself so thatit is elongate in the direction of flow of the current.

Preferably, the body oscillates in a vertical direction.

Preferably, one or more reversible controls members are pivotable in itsentirety.

Preferably, one or more reversible control member are pivotable about anedge protruding from the body.

Preferably, one or more reversible control members are pivotable about acentral axis protruding from the body.

Preferably, one or more of the reversible control members are formed bya pivotable flap mounted to a control member or other mounting meansfixed with respect to the body.

Preferably, one or more reversible control members have an aerofoilshape.

In a further embodiment, one or more control members comprise arotatable cylindrical structure whose direction of rotation can bereversed to generate a change in direction of thrust. As an example, thecylindrical structure may form a continuous cylinder or may have spacedvanes.

Preferably, more than one control member is provided on opposing sidesof the body.

Preferably, the control members are spaced along the body in a directionsubstantially perpendicular to the direction of flow of the water whenthe body is orientated so that its control members protrude from thebody in a direction substantially perpendicular to the direction of flowof water.

Preferably, the body is arranged to oscillate vertically and two or morecontrol members are provided on opposing sides of the body spaced in asubstantially vertical line.

Preferably, three or more control members are provided on each side andthe separation of the control members is substantially equal.

According to a further aspect there is provided, apparatus forextracting power from moving water comprising a prime mover as describedherein.

Preferably, the prime mover is connected to mooring means secured orsecurable under water.

Preferably, the prime mover is connected to mooring cable.

Preferably, the prime mover is axially slidably mounted or mountable toa column secured or securable under water in an upright position.

Preferably, the prime mover comprises a downwardly extending tube whichsurrounds the column.

Preferably, power conversion means are provided for converting theoscillations of the prime mover into another form of power such aselectrical power.

Preferably, the prime mover is submerged when generating power.

Preferably, power conversion means are provided comprising one or morehydraulic pumps, a crank for generating mechanical rotation or means forgenerating electricity such as an electric coil and magnet.

Preferably, power conversion means are provided comprising a fluid pumpfor pumping fluid to a higher level.

Preferably, the apparatus is moored to or mounted on a structure such ascolumn on which apparatus for extracting power from wind or wave ismounted. Thus, the prime mover extracts power from tidal or rivercurrent flow, and power is also extracted from wind or waves. Whilst theprime mover is ideally suited to extracting power from tidal and rivercurrents, it is also adaptable to be used for extracting power fromwaves as will be explained below in connection with a preferredembodiment.

Preferably, the prime mover is buoyant. Typically, it will float on thesurface with part of its structure below the surface.

Preferably, the prime mover comprises an open bottomed tank which whenit oscillates alternately compresses and decompresses a fluid inside itbetween a closed top of the tank and the water surface.

It will be understood by those skilled in the art from the informationdisclosed herein that the inventions in this preferred embodiment canoperate in two modes.

In the first mode, power is extracted from tidal and river flows in thefollowing way. As water flows past the control member, upward anddownward thrust is produced causing the prime mover to move in a planewhich crosses the flow direction (typically it is roughlyperpendicular). Reversing the control member causes the direction ofthrust to be reversed and when this is repeated the prime moverreciprocates generally in the plane.

This reciprocating movement can be converted into a more useful form ofenergy by an appropriate energy removal arrangement. In this preferredembodiment the prime mover is a tank which alternately compresses anddecompresses a fluid.

In the second mode, power is extracted from waves. As waves impinge onthe tank, the water level inside it rises and falls relative to the topof the collector. Vertical movement of the tank is damped by the drag ofthe hydroplanes. This drag can be supplemented, though this is notalways necessary, by reversing the control member or members to producethrust in a direction opposite to the rise and fall of water in thewaves. Thus the tank tends to remain stationary relative to a fixedpoint, the shore or sea bed say, but the fluid inside the tank isalternately compressed and decompressed by the action of the waves.

Preferably, at least one duct in the top of the tank permits the fluidalternately to flow out of and into the tank.

Preferably, the fluid flowing through one or more ducts drives aturbine. Preferably, the turbine is mounted on the tank. Thus, theturbine operates in air when the fluid chosen is air. Preferably, theturbine is directly drivably connected to an electrical generator.

Preferably, the number and/or size of ducts open at any time, orselected to drive a selected turbine at a particular time, can be variedso that the flow of air can be optimized to the efficiency requirementsof the turbine.

Preferably, a turbine is housed in a duct. Preferably, a generator, orcombined turbine and generator is housed in the duct.

Preferably, the turbine rotates in the same direction irrespective ofthe flow of fluid out of or into the tank.

Preferably, valve means are provided so that fluid passes through theturbine in the same direction irrespective of the flow of fluid out ofor into the tank.

Preferably, the fluid is air.

In a further aspect there is provided a method of extracting power frommoving water comprising repeatedly reversing the direction of thrustgenerated by a submerged control member protruding from a body in aprime mover as described herein.

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings as follows:

FIG. 1 is a perspective view of an active water column apparatusinstalled in working position for extracting power from moving water.

FIG. 2 is a plan view of the apparatus of FIG. 1.

FIG. 3 shows eight cross-sectional views (A-H) showing the operatingcycle of the apparatus.

FIG. 4 is a graph showing hydroplane movement, air pressure andhydroplane acceleration as a function of time during the operatingcycle.

FIG. 5 shows a number of repeated cycles similar to those in FIG. 4.

FIG. 6 is a plan view of an alternative embodiment of the inventionshowing several air exhaust/inlet ducts.

FIG. 7 is a cross-sectional view through the apparatus of FIG. 6 showingits mooring on a monopile.

FIGS. 8A and 8B show plain and cross-sectional views of a cable mooredapparatus.

FIGS. 9A and 9B shows cross-sectional views through alternativehydroplanes of the apparatus in accordance with the invention.

FIG. 10 is a schematic elevation view of one side of an apparatusaccording to the invention showing fixed hydroplanes at a centrallocation and rotatable tail hydroplanes located, in this preferredembodiment, towards the rear of the apparatus vis a vis the flowdirection of the water.

FIG. 11 is a perspective view of a tank according to the inventionshowing optional elongated bearings used to mount the tank to amonopile. Spaced ring bearings may also be used as shown in crosssection in FIG. 7.

FIG. 12 shows a schematic side view of a tank detailing the use ofcontrol members as water reflectors rather than hydroplanes.

FIGS. 13A and 13B show a plan view of a tank according to inventionmoored by cables when tidal flow in and out are at 180 degrees andmoored by a monopile when tidal flow is at an angle B between inward andoutward flows, respectively.

FIGS. 14A and 14B show plain and cross-sectional views of an apparatusfor generating power from a prime mover according to the invention usinga hydraulic cylinder when moored to a monopile support column.

FIGS. 15A and 15B are similar to FIGS. 14A and 14B, but acontrol/generating box is floating beneath the surface and moored bycables.

FIGS. 16A and 16B show plain and cross-sectional views of an apparatusfor generating mechanical power from a submerged prime mover moored on amonopile support column. The apparatus can be rearranged in a similarmanner to that of FIGS. 15A&B, ie. utilising a control/generating boxsubmerged and moored by a cable.

FIG. 17 shows a schematic elevation view of apparatus for generatingelectricity directly using a prime mover.

FIG. 18 shows a schematic elevation view of apparatus for pumping waterto a higher level for storage of potential energy. Typically, the wateris the same as that flowing past the tank 10.

FIG. 19 shows a schematic perspective view of an alternative tank inaccordance with the invention.

In FIG. 1, a large buoyant or floating open bottomed tank 10 containsair as a working fluid (see 17 in FIG. 3). Tank 10 has a substantiallyflat top 12 and is canoe shaped in plan view. The convex sides 14 oftank 10 meet to provide a pointed edge. The sides serve to orientate thetank so that the pointed edge points into the flow so that water passesover convex sides 14. Thus, water travels over sides 14 between pointsP, Q and R. At point Q the flow of water is generally homogenous and istypically faster than the flow of water at points P and R because of theconstriction produced by the widening of the tank at that point. This isa suitable point at which to place hydroplanes 22 protruding from sides14, the kinetic of the water energy available to be extracted beingproportional to the cube of the velocity of the flow. Therefore thehydroplanes are advantageously located at this point of maximumvelocity.

Tank 10 typically comprises a downwardly extending tube (not shown)which slidably surrounds a support column 16 secured underwater, usuallyto the sea or river bed 18, in an upright position. Typically, a largediameter bearing 20, for example a plane bearing, is secured in the topof the tube and a similar bearing (not shown) is secured in the bottomof the tube so that the two bearings are widely spaced apart. Thus, saidbearings are slidable axially and rotateably relative to the column 16.Further bearing strips may be provided as an alternative or in additionto the circular bearings as shown in FIG. 11.

Hydroplanes 22 are submerged and pivotable in their entirety, typicallyabout a lower edge 23, about an axis generally perpendicular to sides 14of the tank. The two upper hydroplanes 22 on opposite sides 14 of thetank are interconnected by a shaft (not shown) and the two lowerhydroplanes are likewise interconnected. The inclination of thehydroplanes 22 is reversible in unison by partially rotating theassociated shafts, for example by hydraulic or mechanical means. Suchchange in the inclination of the hydroplanes is typically undercomputerised control and in response to several parameters. Theseparameters include motion of the tank, water flow direction, forces onthe hydroplanes and/or air pressure in the tank. As will be explainedbelow, the optimum arrangement is such that air is virtually alwaysflowing into or out of the tank. The energy within the tank at a giventime is equivalent to the air pressure times the air volume. The energyavailable to be collected is equivalent to the volume change over agiven time period times the pressure differential over the same period.

The maximum angle of inclination of the hydroplanes 22 is alsoadjustable. Whilst hydroplanes 22 typically act as hydroplanes causinglift by the action of water flowing over their upper and lower surfaces,control members, for example hydroplanes 22, can be caused to act aswater deflectors much in the same way that a kite deflects air. This isshown in FIG. 12 and will be described in further detail later.

Two ducts 25 are formed in the top 12 of tank 10. These ducts house highspeed air turbines and, optionally, also generators which are directlydrivable by the flow of air into and out of the tank and can supplyrotation directly to the electrical generators (not shown)wherever theseare located. Turbines 24, and the generators, need not therefore belocated underwater but are working in air enhancing reliability, andease of maintenance. Valve means (not shown) can be provided in eachduct so that air passes through each turbine 24 in the same directionirrespective of the flow of air into or out of the tank. Alternatively,a special turbine such a Wells turbine is used, such turbines alwaysturn in the same direction irrespective of the direction of air flow.

In operation, the shape and in particular the convex sides 14 of tank 10automatically orientate it like a weather vane so that control members,for example hydroplanes 22, are kept substantially at right angles tothe water current indicated by arrow 26. This orientation reduces dragon the tank and increases the velocity of the current passing alongparticularly the widest most portion of the sides and therefore overhydroplanes 22.

The action of water current indicated by arrow 26 on hydroplanes 22causes the tank to move upwards and downwards on column 16 dependingupon the inclination, for the time being, of the hydroplanes. Thus, thetank is caused to oscillate as indicated by arrow 32 so as toalternately compress (as it moves downwards) and decompress (as it movesupwards) the air contained inside it between top 12 and water surface28.

As tank 10 moves downwards the pressure differential causes air to beexpelled through the ducts. During the downward part of the cycle, thedownward force from hydroplanes 22 and the weight of the tank opposesthe buoyancy forces, ie upthrust of the water on the tank. This can beseen in steps a and b of FIG. 3. The air pressure inside the tank isgreater than atmospheric pressure outside and causes a small change h inthe level of water inside the tank compared to the level of wateroutside the tank. This head of water coupled with further downwardmovement of the tank by virtue of the angle of inclination of thehydroplanes causes the continued pressure differential inside andoutside the tank. Air 30 is expelled from the tank via ducts 25. As canbe seen in FIGS. 4 and 5, at T=T1 air commences to be expelled from thetank. This continues until T=T3 when the downward forces on the tank arebalanced by the upward forces of water, head h of water is lost and thepressure inside the tank equals atmospheric pressure. At this point flow30 ceases. It is desirable that the length of time spent at this pointis kept to a minimum.

Therefore, towards the bottom of the movement and preferably before toolong is spent at the bottom of the movement, the inclination of thehydroplanes 22 is caused to reverse so that these exert a verticalupward force. Tank 10 is accelerated upwards by a combination of thisforce and its buoyancy (see step E in FIG. 3).

As the tank moves upwards, the pressure within it falls belowatmospheric and a small head of water h is developed compared to thelevel of water outside the tank. Air is drawn in through the ducts (seestep F). At the top of the movement the head of water h disappears andthe pressure inside the tank again reaches atmospheric.

Thus, if the distance of the tank above water surface 28 at rest is X1and below water surface 28 is X2 then at step G, the top of the motion,X1 has increased in relation to X2.

In the measurements shown in FIG. 4 there is no peak in the pressuremeasurement to indicate air flowing in to the tank because of thelimitation of the measuring equipment. Nevertheless, air was observed toflow into the tank during the period indicated.

The cycle is repeated beginning again with hydroplanes 22 being inclinedin the other direction with respect to the current indicated by arrow26.

The velocity of the air passing through the turbines can be varied bychanging the size and/or the number of ducts. Thus, in FIG. 6, of thesix ducts shown, one or more of these may be closed off or otherwiseremoved from the flow of air so that the velocity of air passing throughthe remaining ducts is increased. Thus the size and/or number of theducts can be varied so customising a particular apparatus for aparticular location (since current flows vary from location to location)or for particular conditions. Indeed, several ducts can be divertedthrough a single turbine, so that it operates in its most effectiverange for power generation, when water flow is slow, and rediverted toseveral ducts (and hence several turbines) when water flow is fast.Typically, the air turbines also comprise a generator located in theducts. The velocity of air passing through the turbines can also bevaried by changing the number and/or size of the hydroplanes. Thisability to customise the tank to location and the prevailing conditionsallows it to operate at optimum or near optimum efficiency in givencircumstances.

Since the tank 10 floats and is slidable relative to column 16 it isself-adjusting to changes in the height of water surface 28.Furthermore, since it can rotate on column 16, which may be a monopile,it is self-adjusting to changes in the direction of water flow. This canbe particularly important for tidal flows where inward and outward tidalflows are not at approximately 180 degrees to each other. This is shownin detail in FIGS. 13A and 13B in which cables 33 can be used to moortank 10 on monopiles 35 when inward and outward flow are insubstantially opposite directions or in river flows. A limited amount ofrotation can be possible when using mooring cables if the attachmentpoints of the cables are designed for this. However, a central column 16or monopile is typically used to mount tank 10 when inward and outwardflows are at angle B with respect to one another. This allows rotationof tank 10 by angle B to align itself with the prevailing tidal flow.

The angle of inclination of the hydroplanes relative to the directionand speed of the water current governs the magnitude of lift and dragforces on the tank. Thus, typically control members, for examplehyroplanes 22, function as hydroplanes generating lift but little drag.In FIG. 12, water flow indicated by arrow 26 is redirected downwards bycontrol member 22D causing tank 10 to move in the direction of arrow 32.This Is similar to the way that a kite maintains it height. Controlmember 22D is rotated through a vertical plane about a horizontal axisto cause the tank 10 to reverse its direction of motion. Control members22D can however cause drag so their use may be limited to particularcircumstances where drag is not a problem, such as when firm cablemoorings are available.

Adjustment of the angle of hydroplanes or control members 22 d such asthose in FIG. 12 can allow for maximum power output over a wide range ofcurrent speeds. Thus there are several variables as described abovewhich can be optimised to increase the efficiency and power output ofthe apparatus. Furthermore, the apparatus can be connected to shore by apower cable and can be submersible during storms thereby reducing therisk of damage.

FIG. 6 shows control members 22C and 22B which typically function ashydroplanes operating over an angular range of 5 to 30 degrees, forexample, 2α equals around 60 degrees. The frequency with which theplanes are reversed is typically 5 to 20 seconds, but may be less thanor more than this. The angular orientation of the hydroplanes in aworking position is selected from a range of angular working positions.

Hydroplanes or control members 22 a are located on the widest portion oftank 10. Alternative or further hydroplanes or control members 22B and22C can be located at other points though this is less preferred.Hydroplanes or control members 22B are equally spaced whereashydroplanes or control members 22 c are not equally spaced. By locatinghydroplanes in a vertical direction, one above the other, roughlyperpendicular to the water flow the turbulence flow produced downstreamdoes not interfere with its neighbours. Thus, typically one of thehydroplanes or control members 22A and 22B and 22C, is selected ratherthan having hydroplanes spaced along the tank in the direction of flowof the water. The hydroplanes may be staggered, i.e. spaced verticallybut overlapping in a horizontal direction such as hydroplanes 22E inFIG. 8.

FIGS. 8a and 8 b also show a tank similar to that in FIG. 6 and 7 butmoored by cables 33 to a suitable mooring point either above or belowwater level. FIG. 9A shows two symmetrical cross-sections, one moreaerodynamic than the other, for use as hydroplanes and one aerofoilcross-section for use as hydroplane. Typically, symmetrical shapes arepreferred and aerodynamic shapes are preferred most of all.

FIG. 10 shows fixed hydroplanes 22 which do not rotate with respect totank 10. Rotatable tail hydroplanes 34 cause the tank to rise or fall.Once this rise has begun, it slightly tilts the tank so that hydroplanes22 are now at an angle with respect to water flow 26 thus adding to theforces causing the tank to rise or fall. Other hydroplanes, or mountingstructures, fixed with respect to the tank on which reversiblehydroplanes are mounted may be used. These resemble pivotal flaps onaeroplane wings. A further type of hydroplane suitable for use with theinvention is shown in FIG. 9B. Here, hydroplane 22F shown in crosssection is flexible and can be flexed so that its curvature is inverted(reversed) causing lift 32A or downward thrust 32D as appropriate.

FIGS. 14A-B, 15A-B, 16A-B, 17 and 18 show the use of a prime mover 40mounted about a column 16 or moored via cables 33 and provided withhydroplanes 22 causing prime mover 40 to rise or fall on the reverse ofthese hydroplanes. Several different kinds of power conversion means areprovided for converting the oscillating motion of prime mover 40 intousable forms of power, whether this is water stored at a higher level,mechanical rotation, electrical power, hydraulic power and so on. Whisttank 10 is typically buoyant, prime mover 40 is typically partiallybuoyant so that it is submerged when at rest. Prime mover 40 rises andfalls in exactly the same way as tank 10 by reversing the inclination ofhydroplanes 22 or control members 22D as previously described. Thus,prime mover 40 oscillates up and down in the direction of arrow 32.

In FIGS. 14a and 14 b, a hydraulic piston pumps fluid within a controlchamber 44 to generate power or connects to a crank.

In FIGS. 15a and 15 b, a similar hydraulic pump 42 is used though inthis case control chamber 44 is located beneath the surface and ismoored to the sea bed by cables 33. Thus, the prime mover 40 here floatsabove the sea bed. Typically column 16A, about which prime mover 40 islocated, comprises slots through which members mounted on prime mover 40project to drive pump 42 so causing the piston in hydraulic apparatus 42to rise and fall. Also column 16A is open to the surface to permitaccess to the control chamber 44 and so that power can be extracted forexample by cables.

In FIGS. 16a-16 b, shaft 42 a rises and falls causing a crank system 43to generate mechanical rotation which can be converted into electricalpower or caused to drive a turbine.

In FIG. 17 struts 46 carry a coil 48 and move up and down in thedirection of arrow 32 along with prime mover 40. Coil 48 is positionedabout a magnet 50 to provide directly an ac current directly.

In FIG. 18, water is pumped by hydraulic apparatus 42 and pipe 52 intoan elevated storage chamber 54. The water falls back via pipe 56 and canbe used to generate electrical power in water turbine 58.

In FIG. 19, an alternative embodiment uses rotating cylinders togenerate upward and downward thrust. Cylinders 61 rotate in thedirection of arrow 63 with respect to current 26. The cylinders producedrag 62 but also a downward force 60, or an upward force when rotationis reversed. Whilst rotation may be produced by driving connecting rod64 using electricity, current 26 may be used to provide the necessaryrotation via rotating wheel 70 which via connecting means 68 and gearbox 66 causes rod 64 to rotate. A windmill type wheel rotating about ahorizontal axis (not shown) could also be used. The gear box could beused to produce the reversal in rotation 63 without changing thedirection of motion of rotating wheel 70.

Thus, the invention provides not only an apparatus for converting slowmoving water or other suitable fluids (both gases and liquids) into fastmoving air so that rotational speeds of 1,000 to 3,000 revolutions perminute in turbines can be generated, but also prime movers which can becombined with any appropriate energy removal system. Suitable liquids orother gases can be used in place of air. The fast moving fluid istypically lighter than the fluid from which power is extracted. The tankcan be non-buoyant or of neutral buoyancy. The tank or prime mover canbe orientated by power driven means instead of like a weather vane. Oneor more rudders or other vertical control surfaces may be provided toaid the orientation of the tank. These may be power driven but could bemanually set for example on each tide change. The tank and the primemover can be located permanently under water. The tank can have a shapedifferent from that shown. A single tank or several tanks may be used.

The apparatus can be used to provide power for an associateddesalination plant. One further arrangement is for a combined apparatusresponsive to tidal flows, waves and windpower is provide. For example,a wind turbine mounted on top of a support column could be used. Thuspower generation is derivable from the action of wave energy on theprime mover, especially when the prime mover is a tank, tidal flows onthe prime mover and wind power from the wind turbine mounted on top ofthe support column. Power generation is possible from the action ofwaves on one of the control surfaces providing resistance to the bobbingmotion of the tank under the influence of the waves. Power generationfrom waves incident on the semi buoyant collector cause the water insidethe collector level to rise and fall relative to the top of thecollector. Vertical movement of the collector is damped by the drag ofthe hydroplanes. The force of the moving water in the wave cycle pushingagainst the hydroplanes can cause the collector to move in oppositephase to the water inside the collector so causing the fluid in it to bealternately compressed and decompressed. The angle of the hydroplanescan be altered to increase this effect of the waves passing into thecollector. The apparatus can incorporate means for storage of energy orcan be used to provide power for an autonomous device such as a buoy. Afurther embodiment may include two prime movers such as tanks 10 withone or more hydroplanes extending between the prime movers. This offersstability to the hydroplanes since both ends of each hydroplane aresupported by the tanks.

Control members in the form of hydroplanes and rotating cylindricalstructures (whether hollow, solid or vanes spaces about roughlycylindrical periphery and so on) can be used in combination on a primemover of the invention. The prime mover may be arranged to oscillatehorizontally. The angle of inclination, need not be the same for theupward and downward parts of this cycle (eg to take account of theweight of the prime mover).

What is claimed is:
 1. A prime mover adapted for submersion in a currentof water for extracting power from the current of water comprising: (a)a body; (b) first and second hydroplanes mounted on the body andextending from respective sides thereof, the angle of inclination of thehydroplanes with respect to said current flow being operativelychangeable by rotation of the hydroplanes in unison about a common axiswhich axis passes through the body and which axis is substantiallyperpendicular to the direction of flow of the current, the hydroplanesbeing operatively rotatable in unison about said axis between: (i) firstpositions in which the angle of inclination is such that the action ofthe current on the hydroplanes is effective to generate thrust in afirst direction and thereby to move the body in said first direction and(ii) second positions in which the angle of inclination is such that theaction of the current on the hydroplanes is effective to generate thrustin a second direction opposite to the first direction and thereby tomove the body in said second direction; (c) means for rotating thehydroplanes from a said first position to a said second position whenthe body is moving in the first direction and for rotating thehydroplanes from a said second position to a said first position whenthe body is moving in the second direction thereby causing the body toexecute a controlled oscillation; and (d) means for extracting powerfrom the oscillatory movement of the body.
 2. An apparatus forextracting power from moving water comprising the prime mover accordingto claim
 1. 3. A method for extracting power from a current of waterusing a prime mover as claimed in claim 1, comprising: submersing saidbody in said current of water; and periodically reversing the directionof thrust generated by the said hydroplane, by operating said means forrotating the hydroplanes.